An organic light emitting device is a device in which a thin film including a fluorescent organic compound is sandwiched between an anode and a cathode. Further, electrons and holes are injected from the respective electrodes to generate exciton of the fluorescent compound, whereby the organic light emitting device emits light when the exciton returns to a ground state.
Recent progress of an organic light emitting device is remarkable, and the characteristics of the device enable a light emitting device with a high luminance at a low applied voltage, a variety of emission wavelengths, high-speed responsiveness, thin and light weight. From this fact, it is suggested that the organic light emitting device have potential to find use in a wide variety of applications.
However, the present situation calls for optical output with even higher luminance or higher conversion efficiency. In addition, many problems still remain to be solved regarding durability against the change over time due to long-term use, deterioration caused by atmospheric gas containing oxygen, moisture, or the like.
Further, when considering application to a full color display or the like, the present art is still insufficient against problems relating to the needs for light emission of a red color with high color purity and high efficiency. On the other hand, an organic light emitting device having, in particular, high color purity, high light emitting efficiency, and high durability, and a material realizing the organic light emitting device have been demanded.
By the way, as a light emitting material which can utilize light emission from a triplet excitation state, an iridium (Ir) complex has been proposed. Examples of the Ir complex to be used as the light emitting material herein include the Ir complexes disclosed in Macromol. Symp. 125, 1-48 (1997), “Improved energy transfer in electrophosphorescent device”, D. F. O'Brien, et al., Applied Physics Letters, Vol. 74, No. 3, p. 422 (1999), “Very high-efficiency green organic light-emitting devices based on electrophosphorescence”, M. A. Baldo, et al., Applied Physics Letters, Vol. 75, No. 1, p. 4 (1999), Japanese Patent Application Laid-Open No. 2001-247859, and Japanese Patent Application Laid-Open No. 2005-344124.